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values and valueOf

Learn enum operations with values() and valueOf().

values returns all constants

values() returns all constants of an enum as an array. valueOf(String) obtains a constant from a name. These are the core tools for looping and conversion.

for (Day d : Day.values()) {
  System.out.println(d);
}
Day d = Day.valueOf("MONDAY");

values() creates a new array on each call, but for small enums this does not matter. valueOf throws IllegalArgumentException if the name is not found, so you should validate input. Together they make it easy to iterate over an enum.

Iterate constants with for-each

The array returned by values() makes a for-each loop easy to write. This is the most common way to list all options of an enum.

for (Day d : Day.values()) {
  System.out.println(d + " " + d.ordinal());
}

The loop order matches the declaration order, so the output is predictable. This pattern is very handy for listing menu options or processing all states. You can also access the ordinal with ordinal().

Practice List all days

Define the Day enum (MONDAY through SUNDAY). Build a for-each loop over values() and print each day on its own line.

Starter code

Main.java
public class Main {
  public static void main(String[] args) {
    // Define the Day enum, loop with values(), print
  }
}

// Define the Day enum here

Sample solution

Main.java
enum Day { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY }
// inside main:
for (Day d : Day.values()) {
  System.out.println(d);
}

Expected output

MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
SUNDAY

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does Day.valueOf("MONDAY") return?

  • An array
  • The string "MONDAY"
  • 0
  • The Day.MONDAY constant Correct answer

Explanation: valueOf obtains an enum constant from a name; it returns the constant itself, not a string.

2 Match each method to its return type

Term Meaning
values() Day[]
valueOf(String) Day
ordinal() int
name() String

3 Find a constant with valueOf

Question 
Day d = Day.____("MONDAY");
Answer 
Day d = Day.valueOf("MONDAY");

Explanation: valueOf produces a constant from a name.

All lessons in Beginner

1 Java basics

  1. What is Java?
  2. The main method
  3. Comments
  4. Class skeleton
  5. javac and java
  6. Summary - Java basics

2 Variables

  1. int and double
  2. boolean
  3. String
  4. Naming variables
  5. final variables
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Type casting
  3. String concatenation
  4. Math class
  5. BigInteger and BigDecimal
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Assignment and increment
  6. Summary - Operators

6 String basics

  1. length and charAt
  2. equals and equalsIgnoreCase
  3. indexOf and substring
  4. toUpperCase and trim
  5. String.format
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and else if
  3. Nested if
  4. switch
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. do-while
  4. break and continue
  5. for-each
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Filling arrays
  4. Multi-dimensional arrays
  5. Copying arrays
  6. Summary - Arrays

11 Array methods

  1. Arrays.sort
  2. Arrays.toString
  3. Arrays.binarySearch
  4. Arrays.copyOf
  5. Arrays.fill
  6. Summary - Array methods

12 Collections

  1. ArrayList
  2. add and get
  3. HashMap
  4. put and get
  5. HashSet
  6. Summary - Collections

13 Methods

  1. Defining methods
  2. return
  3. void methods
  4. Method overloading
  5. Scope
  6. Summary - Methods

14 Method parameters

  1. Primitive parameters
  2. Object parameters
  3. varargs
  4. Multiple values via array
  5. final parameters
  6. Summary - Method parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String builder

  1. StringBuilder
  2. append
  3. insert and delete
  4. reverse
  5. toString
  6. Summary - String builder

17 Input and output

  1. Scanner
  2. nextInt and nextLine
  3. System.out.printf
  4. BufferedReader
  5. try-with-resources
  6. Summary - Input and output

18 Enum

  1. Declaring enums
  2. values and valueOf
  3. Enum fields
  4. Enum methods
  5. switch with enum
  6. Summary - Enum

19 Exception basics

  1. try/catch
  2. finally
  3. throw
  4. Exception hierarchy
  5. Multiple catch
  6. Summary - Exception basics

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together